The future of the Rugby World Cup will come under threat unless fundamental changes ensure leading nations do not lose millions in revenue at the 2015 tournament in England, according to the head of the New Zealand Rugby Union.

Steve Tew, the NZRU chief executive, has warned that competing at the World Cup has cost his union more than NZ$13m (£7m), a loss it could ill afford at a time when player costs were rising and the world economy was stagnating. Incoming tours are halted in a World Cup year and competing nations are not allowed to have any association with their sponsors for the duration of the tournament.

The International Rugby Board will by next May complete a review of how the World Cup is run. Tew said that unless changes were agreed, he feared his union, which is hosting this year's tournament, would not be able to afford to take part in the 2015 event.

"We think we are at a really important juncture," he said. "We want a couple of things taken very seriously around the IRB table. One is the money that flows through and out of Rugby World Cup. It is well publicised that the major unions lose a significant amount of money net by participating in the tournament and that makes absolutely no sense.

"We lose NZ$13.2m [£6.7m] worth of revenue after income from Rugby World Cup and costs are adjusted. It cannot carry on. We said at the last board conference that we needed a full review of the IRB's financial model, Rugby World Cup commercial rules and RWC money flows. We are waiting with some anxiety what the IRB are going to do about it.

"The IRB did put an extra £1m on the table for the major unions six months ago which helped and which was appreciated, but frankly the prospects of us going to England in 2015 under the current model are very slim. We cannot continue to sign on for an event that costs us so much money.